The invention relates generally to material feeding systems and more particularly to dry solid feeding systems.
The precise metering of dry solids is important in many applications, including numerous manufacturing processes in various industries. Usually when material is continuously metered into a process, it must be precisely controlled at a specific feed rate so that the process functions as designed, the product formulation is correct, and the quality of the end product of the process does not suffer.
Various kinds of weigh feeders have been used for weighing and feeding dry solids such as sand, gravel, grain, foodstuffs, chemicals, pharmaceuticals, ceramics, etc. In general, material is provided to a weigh feeder continuously or periodically and the weigh feeder discharges the material at a continuous and constant output rate. Different weigh feeders, however, have different capabilities, which depend on the design of the weigh feeder and its principle of operation. Weight-loss, weigh belt, and weigh auger feeders are three types of commonly used weigh feeders.
Weigh belt feeders weigh material as the material is transported by a moving belt and require a continuous supply of material, generally from an overhead storage supply. In one functional configuration (e.g. Acrison, Inc., Model 260 Belt Weigher/Feeder), material travels from a storage supply, down a chute and onto a rear portion of the belt, which is not weighed. As the belt moves, the material on the belt passes over a weighing section, and a weight signal is produced that corresponds to the weight of material traveling across the weighing section. The weight signal is processed in conjunction with another signal, representing the speed of the belt, by the weigh feeder""s controller to derive a feed rate signal. The feed rate signal is compared to the feed rate desired by the user, and the weigh feeder""s controller continuously adjusts a variable speed drive powering the belt to maintain the desired feed rate.
A weigh belt feeder may also utilize a feeding mechanism to actively feed material onto the belt (e.g. a screw conveyor/feeder, another belt, a vibratory tray device, etc.). Although such active feeding (or prefeeding) is different from the method of gravimetric feeding described above, the material on the belt is weighed in an identical manner. Such active feeding of material onto the weigh belt generally provides a greater degree of physical control over the material being fed. In this mode of operation, the weigh belt moves at a fixed constant speed, and the feed rate of the feeding mechanism is variable. Thus, the weigh feeder""s controller continuously modulates the output of the feeding mechanism that feeds material onto the belt to maintain a selected feed rate of material off the belt. Material is usually provided to the feeding mechanism directly from a storage supply, for example, a hopper or silo.
A different type of weigh belt feeder (e.g. Acrison, Inc., Models 203/210) operates by weighing the entire weigh belt assembly, while a pre-feeder (e.g. a screw conveyor/feeder, another belt, or a vibratory type device) meters material onto the weigh belt, which operates at a fixed constant speed. The output of the pre-feeder, which is equipped with a variable speed output drive, is continuously modulated by the weigh feeder""s controller so that the rate at which material passes across the weigh belt accurately matches the selected feed rate. In such a weigh feeder, material is also usually supplied to the pre-feeder directly from a storage supply.
A weigh auger feeder (e.g. Acrison, Inc., Model 203B) operates in a manner similar to the weigh belt described immediately above, except that an auger, rather than a belt, is used to weigh and convey the material.
A weight-loss feeder (e.g. Acrison, Inc. Model 400 Series) comprises a material supply hopper and a feeding mechanism mounted on a scale. As material is fed out of the scale-mounted metering/supply system, a decreasing weight signal is produced, which is processed by the weigh feeder""s controller in conjunction with a time signal to calculate a feed rate. The feeding mechanism of a weight-loss weigh feeder is equipped with a variable speed drive so that its feed rate output can be continuously modulated by the weigh feeder""s controller in order to maintain the selected feed rate. The supply hopper of a weight-loss weigh feeder can be periodically refilled.
In a first aspect, the invention features a weigh feeding apparatus having a plurality of compartments to hold a material that is fed into the compartments and a scale for weighing the material held in the compartments. The compartments are configured to revolve about an axis at a substantially constant rate and the scale is configured to produce a signal determined by the weight of the material held in the compartments. The signal is capable of being used to control the rate at which material is fed into the compartments.
Implementations of the invention may include one or more of the following. The compartments may include at least two vanes that radiate from an axle. The compartments may be configured to move from a first position to a second position, where the compartments are capable of receiving material fed into the compartments when the compartments are in the first position and are capable of discharging material when the compartments are in the second position. The signal may be capable of being used to control the rate which material is material is fed into the compartments, such that the weight of the material in the plurality of compartments is held substantially constant as the material is discharged from the compartments in the second position. The compartments may be configured to discharge material at a substantially constant discharge rate.
In an additional implementation, the invention may include a pre-feeder to feed material into the compartments, where the pre-feeder is capable of receiving the signal from the scale. The pre-feeder may be configured to feed material into the compartments at a rate determined by the signal from the scale. The compartments of the rotatable compartmented mechanism may be configured to move from a first position to a second position, and the compartments may be capable of receiving material fed into the compartments from the pre-feeder when the compartments are in the first position and may be capable of discharging material when the compartments are in the second position. The signal may be capable of being used to control the feed rate of the pre-feeder, such that the weight of the material in the plurality of compartments is held substantially constant as the material is discharged from compartments in the second position while the material is discharged from the rotatable compartmented mechanism at a substantially constant discharge rate.
In a second aspect, the invention features a method for providing a material at a substantially constant rate by feeding the material from a pre-feeder into a plurality of compartments for holding the material, as the compartments revolve about an axis at a substantially constant speed; weighing the material held in the plurality of compartments; providing a signal determined by the weight of the material held in the plurality of compartments; and using the signal to adjust the feed rate of the pre-feeder.
Implementations of the invention may include one or more of the following. The signal may be an electrical, mechanical, or optical signal. The material may be a solid or a liquid. The compartments may include at least two vanes that radiate from an axle and at least two endplates. As the compartments revolve, each of the compartments may move from a first position to a second position, and material may be fed into each of the compartments when the compartment is in the first position and may be discharged from each of the compartments when the compartments are in the second position. The rate at which the feeder feeds the material into the compartments may be adjusted, such that the weight of the material in the plurality of compartments is held substantially constant as the compartments revolve.